Universe Today

Image credit: NASA

Wide-field observations of the early Universe have turned up a strange string of galaxies 300 million light-years long that defy current theories about the evolution of the Universe shortly after the Big Bang. The astronomers who discovered the string of galaxies, which are more than 10 billion light-years away, compared it to supercomputer simulations of the early Universe, which wasn’t able to reproduce strings this large this early. The next step of this research will be to map an area of the sky ten times as large to get a better idea of the large scale structure of the Universe.

Wide-field telescope observations of the remote and therefore early Universe, looking back to a time when it was a fifth of its present age (redshift = 2.38), have revealed an enormous string of galaxies about 300 million light-years long. This new structure defies current models of how the Universe evolved, which can’t explain how a string this big could have formed so early.

The string is comparable in size to the “Great Wall” of galaxies found in the nearby Universe by Dr. John Huchra and Dr. Margaret Geller in 1989. This is the first time astronomers have been able to map an area in the early Universe big enough to reveal such a galaxy structure.

The string was discovered by Dr. Povilas Palunas (University of Texas, in Austin, Texas), Dr. Paul Francis (Australian National University, Canberra, Australia), Dr. Harry Teplitz (California Institute of Technology in Pasadena), Dr. Gerard Williger (Johns Hopkins University, Baltimore, Md.), and Dr. Bruce E. Woodgate (NASA Goddard Space Flight Center, Greenbelt, Md.). The initial observations were made with the 4-m (159-inch) Blanco Telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile, and confirmed with the 3.9-m (154-inch) Anglo-Australian Telescope at Siding Spring Observatory in eastern Australia. The team presents its finding today at the American Astronomical Society meeting in Atlanta, Georgia, and a paper describing this work will appear in the Astrophysical Journal in February.

The string lies 10,800 million light-years away in the direction of the southern constellation Grus (the Crane). The distance light travels in a year, almost six trillion miles or 9.5 trillion km., is one light-year, so we see the string as it appeared 10.8 billion years ago. It is at least 300 million light-years long and about 50 million light-years wide. (Refer to Movie 1 and Images 3 and 4 for an artist’s concept of the string.) The astronomers have detected 37 galaxies and one quasar in the string, but “there are almost certainly far more than this,” said Palunas. “The string probably contains many thousands of galaxies.” (Refer to Image 1 for an artist’s concept of these galaxies, and to Image 5 for a plot of their locations on the sky.)

“We are seeing this string as it was when the Universe was only a fifth of its present age,” said Woodgate. “That is, we are looking back four-fifths of the way to the beginning of the Universe as a result of the Big Bang.”

The team compared their observations to supercomputer simulations of the early Universe, which could not reproduce strings this large. “The simulations tell us that you cannot take the matter in the early Universe and line it up in strings this large,” said Francis. “There simply hasn’t been enough time since the Big Bang for it to form structures this colossal”.

“Our best guess right now is that it’s a tip-of-the-iceberg effect,” he said. “All we are seeing is the brightest few galaxies. That’s probably far less than 1% of what’s really out there, most of which is the mysterious invisible dark matter. It could be that the dark matter is not arranged in the same way as the galaxies we are seeing.” Recently, evidence has accumulated for the presence of dark matter in the Universe, an invisible form of matter only detectable by the gravitational pull it exerts on ordinary matter (and light). There are many possibilities for what dark matter might be, but its true nature is currently unknown.

In recent years, Francis explained, it had been found that in the local Universe, dark matter is distributed on large scales in very much the same way the galaxies are, rather than being more clumpy, or less. But go back 10 billion years and it could be a very different story. Galaxies probably form in the center of dark matter clouds. But in the early Universe, most galaxies had not yet formed, and most dark matter clouds will not yet contain a galaxy.

“To explain our results,” said Francis, “the dark matter clouds that lie in strings must have formed galaxies, while the dark matter clouds elsewhere have not done so. We’ve no idea why this happened – it’s not what the models predict.”

To follow up this research, the astronomers say, the next step is to map an area of sky ten times larger, to get a better idea of the large-scale structure. Several such surveys are currently under way. The research was funded by NASA and the Australian National University.

Original Source: NASA News Release

Image credit: Harvard CfA

Astronomers from the Harvard Center for Astrophysics studied Comet Kudo-Fujikawa as it swept past the Sun in early 2003, and they noticed it was emitting large amounts of carbon and water vapour. This new view of the comet matches observations of other stars that indicate there could be comets emitting similar material. Since other stars probably have comets, it increases the likelihood that they could also have rocky planets, like the Earth.

In early 2003, Comet Kudo-Fujikawa (C/2002 X5) zipped past the Sun at a distance half that of Mercury’s orbit. Astronomers Matthew Povich and John Raymond (Harvard-Smithsonian Center for Astrophysics) and colleagues studied Kudo-Fujikawa during its close passage. Today at the 203rd meeting of the American Astronomical Society in Atlanta, they announced that they observed the comet puffing out huge amounts of carbon, one of the key elements for life. The comet also emitted large amounts of water vapor as the Sun’s heat baked its outer surface.

When combined with previous observations suggesting the presence of evaporating comets near young stars like Beta Pictoris and old stars like CW Leonis, these data show that stars of all ages vaporize comets that swing too close. Those observations also show that planetary systems like our own, complete with a collection of comets, likely are common throughout space.

“Now we can draw parallels between a comet close to home and cometary activity surrounding the star Beta Pictoris, which just might have newborn planets orbiting it. If comets are not unique to our Sun, then might not the same be true for Earth-like planets?” says Povich.

SOHO Sees Carbon
The team’s observations, reported in the December 12, 2003, issue of the journal Science, were made with the Ultraviolet Coronagraph Spectrometer (UVCS) instrument on board NASA’s Solar and Heliospheric Observatory (SOHO) spacecraft.

UVCS can only study a small slice of the sky at one time. By holding the spectrograph slit steady and allowing the comet to drift past, the team was able to assemble the slices into a full, two-dimensional picture of the comet.

The UVCS data revealed a dramatic tail of carbon ions streaming away from the comet, generated by evaporating dust. The instrument also captured a spectacular ‘disconnection event,’ in which a piece of the ion tail broke off and drifted away from the comet. Such events are relatively common, occurring when the comet passes through a region of space where the Sun’s magnetic field switches direction.

Cometary Building Blocks
More remarkable than the morphology of the carbon ion tail was its size. A single snapshot of Kudo-Fujikawa on one day showed that its ion tail contained at least 200 million pounds of doubly ionized carbon. The tail likely held more than 1.5 billion pounds of carbon in all forms.

“That’s a massive amount of carbon, weighing as much as five supertankers,” says Raymond.

Povich adds, “Now, consider that astronomers see evidence for comets like this around newly formed stars like Beta Pictoris. If such stars have comets, then perhaps they have planets, too. And if extrasolar comets are similar to comets in our solar system, then the building blocks for life may be quite common.”

Understanding Our Origins
In 2001, researcher Gary Melnick (CfA) and colleagues found evidence for comets in a very different system surrounding the aging red giant star CW Leonis. The Submillimeter Wave Astronomy Satellite (SWAS) detected huge clouds of water vapor released by a Kuiper Belt-like swarm of comets which are evaporating under the giant’s relentless heat.

“Taken together, the observations of comets around young stars like Beta Pictoris, middle-aged stars like our Sun, all planets, and old stars like CW Leonis strengthen the connection between our solar system and extrasolar planetary systems. By studying our own neighborhood, we hope to learn not only about our origins, but about what we might find out there orbiting other stars,” says Raymond.

Other co-authors on the Science paper reporting these findings are Geraint Jones (JPL), Michael Uzzo and Yuan-Kuen Ko (CfA), Paul Feldman (Johns Hopkins), Peter Smith and Brian Marsden (CfA), and Thomas Woods (University of Colorado).

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Image credit: RAS

An international team of astronomers have discovered a double pulsar system – the first ever seen. The two objects orbit a common centre of gravity once every 2.4 hours; one rotates at 3000 times a minute, while the other spins at only 22 times a minute. This discovery is important because it will allow astronomers to test various theories of relativity as the two objects interact with each other. The two pulsars will probably merge to become a black hole in 85 million years.

An international team of scientists from the UK, Australia, Italy and the USA have announced in today’s issue of the journal Science Express [ 8th January 2004 ] the first discovery of a double pulsar system.

They have shown that the compact object orbiting the 23-millisecond pulsar PSR J0737-3039A with a period of just 2.4 hours is not only, as suspected, another neutron star but is also a detectable pulsar, PSR J0737-3039B, that is rotating once every 2.8 seconds.

Professor Andrew Lyne of the University of Manchester points out that “While experiments on one pulsar in such an extreme system as this are exciting enough, the discovery of two pulsars orbiting one another opens up new precision tests of general relativity and the probing of pulsar magnetospheres.”

The same team previously reported [Nature 4th December 2003], the discovery of pulsar A in a close binary system which is rapidly losing energy by gravitational radiation. The stars will coalesce in only approximately 85 million years, sending a ripple of gravity waves across the Universe. The discovery of the system shows that such coalescences will occur more frequently than previously thought. “The news has been welcomed by gravitational wave hunters, since it boosts their hopes for detecting the gravitational waves” says Prof. Nichi D’Amico of Cagliari University.

The double neutron star system was first detected using the 64-m Parkes radio telescope in New South Wales, Australia. Subsequent observations were made both at Parkes and with the 76-m Lovell Telescope of the University of Manchester in Cheshire, UK and revealed the occasional presence of pulsations with a period of 2.8 seconds from the companion pulsar.

Already, four different effects beyond those explained with simple Newtonian gravity have been measured and are completely consistent with Albert Einstein’s theory. Dr. Richard Manchester of the Australia Telescope National Facility says “The fact that both objects are pulsars enables completely new high-precision tests of gravitational theories. This system is really extreme.” Future observations of the two stars will measure their slow spiral in towards each other as they radiate gravitational radiation – a dance of death leading to their ultimate fusion into what may become a black hole. General relativity predicts that the two stars will slowly wobble like spinning tops allowing new tests of the theory.

Another unique aspect of the new system is the strong interaction between radiation from the two stars. By chance, the orbit is seen nearly edge on to us, and the signal from one pulsar is eclipsed by the other. Dr. Andrea Possenti of Cagliari Astronomical Observatory says “This provides us with a wonderful opportunity to probe the physical conditions of a pulsar’s outer atmosphere, something we’ve never been able to do before.”

The surveys designed by the team to discover new pulsars at the Parkes Telescope have been extraordinarily successful. They have discovered over 700 pulsars in the last 5 years, nearly as many as were discovered in the preceding 30 years. The discovery of this double pulsar system will be the major jewel in the crown.

Original Source: RAS News Release

Image credit: NASA

A team of astronomers were lucky enough to observe the rare event of a neutron star turning into a magnetic object called a magnetar. Ten magnetars have been seen to date, but this object, a transient magnetar, is brand new. A normal neutron star is the rapidly spinning remnant of a star that went supernova; they typically possess a very strong magnetic field. A magnetar is similar, but it has a magnetic field up to 1,000 times as strong as a neutron star. This new discovery could indicate that magnetars are more common in the Universe than previously thought.

In a lucky observation, scientists say they have discovered a neutron star in the act of changing into a rare class of extremely magnetic objects called magnetars. No such event has been witnessed definitively until now. This discovery marks only the tenth confirmed magnetar ever found and the first transient magnetar.

The transient nature of this object, discovered in July 2003 with NASA’s Rossi X-ray Timing Explorer, may ultimately fill in important gaps in neutron star evolution. Dr. Alaa Ibrahim of George Washington University and NASA Goddard Space Flight Center in Greenbelt, Md., presents this result today at the meeting of the American Astronomical Society in Atlanta.

A neutron star is the core remains of a star at least eight times more massive than the Sun that exploded in a supernova event. Neutron stars are highly compact, highly magnetic, fast-spinning objects with about a Sun’s worth of mass compressed into a sphere roughly ten miles in diameter.

A magnetar is up to a thousand times more magnetic than ordinary neutron stars. At a hundred trillion (10^14) Gauss, they are so magnetic that they could strip a credit card clean at a distance of 100,000 miles. The Earth’s magnetic field, in comparison, is about 0.5 Gauss, and a strong refrigerator magnet is about 100 Gauss. Magnetars are brighter in X rays than they are in visible light, and they are the only stars known that shine predominantly by magnetic power.

The observation presented today supports the theory that some neutron stars are born with these ultrahigh magnetic fields, but they may be at first too dim to see and measure. In time, however, these magnetic fields act to slow the neutron star’s spin. This act of slowing releases energy, making the star brighter. Additional disturbances in the star’s magnetic field and crust can make it brighter yet, leading to the measurement of its magnetic field. The newly discovered star, dim as recent as a year ago, is named XTE J1810-197.

“The discovery of this source came courtesy of another magnetar that we were monitoring, named SGR 1806-20,” said Ibrahim. He and his colleagues detected XTE J1810-197 with the Rossi Explorer about a degree to the northeast of SGR 1806-20, within the Milky Way galaxy about 15,000 light years away in the constellation Sagittarius.

Scientists pinpointed the location of the source with NASA’s Chandra X-ray Observatory, which provides more accurate positioning than Rossi. Checking archive data from the Rossi Explorer, Dr. Craig Markwardt of NASA Goddard estimated that XTE J1810-197 became active (that is, 100 times brighter than before) around January 2003. Looking back even further with archived data from ASCA and ROSAT, two decommissioned international satellites, the team could spot XTE J1810-197 as a very dim, isolated neutron star as early as 1990. Thus, the history of XTE J1810-197 emerged.

The inactive state of XTE J1810-197, Ibrahim said, was similar to that of other puzzling objects called Compact Central Objects (CCOs) and Dim Isolated Neutron Stars (DINSs). These objects are thought to be neutron stars created in the hearts of star explosions, and some still reside there, but they are too dim to study in detail.

One mark of a neutron star is its magnetic field. But to measure this, scientists need to know the neutron star’s spin period and the rate that it is slowing down, called the “spin down”. When XTE J1810-197 lit up, the team could measure its spin (1 revolution per 5 seconds, typical of magnetars), its spin down, and thus its magnetic field strength (300 trillion Gauss).

In the alphabet soup of neutron stars, there are also Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs). Both of these are now considered to be the same kind of objects, magnetars; and another presentation at today’s meeting by Dr. Peter Woods et al. supports this connection. These objects periodically but unpredictably erupt with X-ray and gamma-ray light. CCOs and DINSs appear not to have a similar active state.

Although the concept is still speculative, an evolutionary pattern may be emerging, Ibrahim said. The same neutron star, endowed with an ultrahigh magnetic field, may pass through each of these four phases during its lifetime. The proper order, however, remains unclear. “Discussion of such a pattern has surfaced in the scientific community in recent years, and XTE J1810-197’s transient nature provides the first tangible evidence in favor of such a kinship,” Ibrahim said. “With a few more examples of stars showing a similar trend, a magnetar family tree may emerge.”

“The observation implies that magnetars could be more common than what is seen but exist in a prolonged dim state,” said team member Dr. Jean Swank of NASA Goddard.

“Magnetars seem now to be in a perpetual carnival mode; SGRs are turning into AXPs and AXPs can start behaving like SGRs anytime and without warning,” said team member Dr. Chryssa Kouveliotou of NASA Marshall, who is receiving the Rossi Award at the AAS meeting for her work on magnetars. “What started with a few odd sources, may soon be proven to encompass a huge number of objects in our Galaxy.”

Additional supporting data came from the Interplanetary Network and the Russian-Turkish Optical Telescope. Ibrahim’s colleagues on this observation also include Dr. William Parke of George Washington University; Drs. Scott Ransom, Mallory Roberts and Vicky Kaspi of McGill University; Dr. Peter Woods of NASA Marshall; Dr. Samar Safi-Harb of the University of Manitoba; Dr. Solen Balman of the Middle East Technical University in Ankara; and Dr. Kevin Hurley of University of California at Berkeley. Drs. Eric Gotthelf and Jules Halpern of Columbia University provided important data from Chandra.

Original Source: NASA News Release